The present invention relates to a cathode ray tube, particularly to an improvement of the white emitting phosphor screen suitable for the monochrome chathode ray tube for terminal display.
Usually, heretofore, for the phosphor screen of white emitting monochrome cathode ray tubes, for instance, a phosphor of the P4 system registered in JEDEC (Joint Electron Device Engineering Councils) is used. As the P4 system phosphor of that case, a phosphor of the ZnCdS system or ZnS system, as single composition, and a mixed phosphor of the ZnCdS system and the ZnS system or of ZnS systems, as mixed system, are mainly used.
However, in the recent cathode ray tubes for terminal display, it has become inevitable to used them with high input and high current density due to the requirement for high resolution and high definition. In such case, there has been caused a problem that long time operation of a cathode ray tube using the above ZnS system phosphor as a blue phosphor increases deterioration of phosphor luminance and burning, and this is not desirable for practical use. Further, CdS system phosphors have such problem to an extent less than ZnS phosphors, but, since it is a cadmium compound, it has a disadvantage that it is not a desirable material in the point of pollution.
As a reference which discloses a white emitting phosphor using a mixed phosphor, the Japanese Patent Publication No. 38490/1985 can be cited.